Researchers have uncovered the existence of “neutronic” molecules, where neutrons can be attached to quantum dots through the strong force. This discovery has the potential to create new methods for studying material properties at the quantum level and developing innovative forms of quantum information processing devices. Neutrons, unlike protons and electrons, are subatomic particles that lack electric charge. As a result, they are unaffected by the electromagnetic force, which is responsible for most interactions between radiation and materials. Instead, neutrons are held in place through the strong force.The strong force holds together the particles inside an atom’s nucleus and is one of the fundamental forces of nature. It is extremely powerful at close range, but its influence diminishes rapidly beyond 1/10,000 the size of an atom. Researchers at MIT have discovered that neutrons can attach to quantum dots, which are made up of tens of thousands of atomic nuclei, solely due to the strong force.
This discovery has the potential to provide new tools for examining the fundamental properties of materials at the quantum level, including those that result from the strong force.of using a neutron beam to probe the behavior of the strong force, or to study quantum information processing devices. The research was published in the journal ACS Nano by MIT graduate students Hao Tang and Guoqing Wang and MIT professors Ju Li and Paola Cappellaro from the Department of Nuclear Science and Engineering.
Neutrons are commonly employed in studying material properties through a technique known as neutron scattering, where a sample is targeted with a neutron beam, and the resulting neutron reflections off the atoms of the material provide insight into its internal structure and dynamics.
However, prior to this study, the idea of using a neutron beam to investigate the strong force or to analyze quantum information processing devices had not been considered.The discovery that neutrons could be captured by the materials they were investigating came as a surprise to researchers. According to Li, a professor of materials science and engineering, this phenomenon was previously unknown to experts in the field. Neutrons typically do not interact with electromagnetic forces, so the fact that they can be trapped by materials is unexpected. Gravity and the weak force are generally not significant for materials, leaving electromagnetic forces as the primary factor to consider.This article discusses the interaction of neutrons within the context of the strong force, as opposed to the electromagnetic force. Since neutrons lack a charge, their interaction is through the strong force, known for its very short range of approximately 10 to the minus 15 power, or one quadrillionth, of a meter.
The intense but small force holds the nuclei of atoms together. The article also addresses the stabilization of bound states within neutronic quantum dots, which contain thousands of nuclei. These bound states have diffuse wavefunctions at tens of nanometers, or billionths of a meter.The state of a quantum dot is very similar to Thomson’s plum pudding model of an atom, which he proposed after discovering the electron.”
The discovery of this state was so unexpected that Li describes it as “a pretty crazy solution to a quantum mechanical problem.” The team has named this newly discovered state an artificial “neutronic molecule.”
Quantum dots are tiny crystalline particles, collections of atoms so small that their properties are governed more by the exact size and shape of the particles than by their composition. The discovery and controlled production of quantum dots were the focus of
The 2023 Nobel Prize in Chemistry was given to MIT Professor Moungi Bawendi and two others.
“In traditional quantum dots, an electron is confined by the electromagnetic potential formed by a large number of atoms, so its wavefunction extends to about 10 nanometers, much larger than a typical atomic radius,” explains Cappellaro. “In the same way, in these nucleonic quantum dots, a single neutron can be confined by a nanocrystal, with a size well beyond the range of the nuclear force, and exhibit similar quantized energies.” While these energy leaps give quantum dots their colors, the neutron quantum dots could be utilized for storing quantum data.”This piece of work is the result of theoretical calculations and computational simulations. According to Li, the team conducted the analysis in two different ways and then confirmed it with numerical verification. Although this effect had not been previously described, Li believes that in theory, it could have been discovered much earlier. He believes that people should have already considered it conceptually, but as far as the team knows, nobody did. One of the challenges in performing these calculations is the significant difference in scales involved, as the binding energy of a neutron to the quantum dots they were connecting to is approximately on a different level.The team discovered that the strong force was able to capture neutrons with a quantum dot with a minimum radius of 13 nanometers, which is a trillionth of the previously known conditions where the neutron is bound to a small group of nuclei. They also conducted detailed simulations of specific cases, such as the use of a lithium hydride nanocrystal, a material being researched for hydrogen storage. The researchers found that the binding energy of the neutrons to the nanocrystal depends on the crystal’s dimensions, shape, and the nuclei.The nuclei have clear spin polarizations compared to the neutron. They also computed similar effects for thin films and wires of the material instead of particles.
However, Li mentions that creating such neutronic molecules in the laboratory, which requires specialized equipment to maintain low temperatures, is a task for other researchers with the necessary expertise to carry out.
Li points out that “artificial atoms” composed of groups of atoms that share properties and can behave similarly to individual atoms.The use of a single atom has been instrumental in exploring various properties of actual atoms. According to the expert, these artificial molecules serve as a fascinating model system for investigating compelling quantum mechanical problems, like determining if these neutronic molecules will exhibit a shell structure resembling the electron shell structure of atoms.
The expert also suggests a potential application, which involves the precise manipulation of the neutron state. By altering the oscillation of the quantum dot, it may be possible to direct the neutron in a specific direction. Neutrons are valuable for tasks such as initiating nuclear fission.The manipulation and control of individual neutrons has proven to be a challenging task, despite advancements in fission and fusion reactions. However, these newly discovered bound states offer the potential for increased control over individual neutrons. This development could have implications for the advancement of quantum information systems, according to Li.
One potential application is the manipulation of neutrons to influence other nuclear spins, serving as a mediator between the nuclear spins of different nuclei. Nuclear spins are already being used as the basis for quantum computing qubits, and this newfound control over individual neutrons could enhance their role in this technology.
“The comparison of nuclear spin to a stationary qubit and the neutron to a flying qubit is very interesting,” he explains. “This presents a potential application that is quite different from the dominant paradigm of electromagnetics-based quantum information processing. Most current systems are based on electromagnetic interactions, such as superconducting qubits, trapped ions, or nitrogen vacancy centers. However, our new system utilizes neutrons and nuclear spin, offering a new approach to explore quantum information processing possibilities.”
Additionally, he suggests that this system could have potential applications in imaging.The use of neutral activation analysis has been described by Li as a way to complement X-ray imaging. Neutrons are much more strongly interacting with light elements, which makes neutron imaging a valuable method for materials analysis. This can provide information not only about elemental composition but also about the different isotopes of those elements. Li also emphasizes that traditional chemical imaging and spectroscopy methods do not provide information about isotopes, whereas the neutron-based method can. The research was supported by the U.S. Office of Naval Research. The journal reference for the study is Hao Tang, Guoqing Wang.μeV-Deep Neutron Bound States in Nanocrystals by Paola Cappellaro and Ju Li was published in ACS Nano in 2024. The article can be accessed through the DOI link: 10.1021/acsnano.3c12929